Homework question. Can anyone help?

The rate of change of atmospheric pressure P with altitude h is given by (dP/dh)=-kP, where k is a constant of proportionality. If the atmospheric pressure at ground level is 15 psi (pounds per square inch) and at 10,000 feet it is 10 psi, find the expression for the pressure as a function of altitude. What is the pressure at 3,000 feet to the nearest hundredth?